1. Field o the Invention
The present invention relates to a graphic editing system for electronic editing of documents and graphic patterns.
2. Related Background Art
In electronic editing systems for documents and graphics, it is often necessary to form the edge of the original image pattern in order to emphasize the effect of the characters and patterns, or to extract the contour of a bit map pattern. A simple method for extracting the contour of a bit map pattern consists of preparing a pattern by taking a logic sum of patterns obtained by moving the original pattern in the vertical and lateral directions by a predetermined amount of bits, and taking a logic exclusive sum of said pattern and the original pattern, thus obtaining the edge of the original pattern.
However such method extracts the external edge (boundary with the non-image area) of the original pattern, so that the ratio of the image area to the non-image area may become different from that of the original image.
In recent years there have been developed electronic phototypesetting systems and electronic editing systems for documents and graphics, utilizing work stations relying on advanced LSI's and laser beam printers capable of reproducing bit map image data of a high resolution. Such systems are required to have various character and graphic patterns, namely various characters, various font styles and various output sizes, and, for achieving such objective inexpensively, there have been proposed, for example, run-length compression of bit pattern and vector encoding of character patterns. The vector encoding is recently getting popularity, as the above-mentioned requirement is difficult to satisfy if the pattern is given by a bit pattern, regardless of the method of data compression. However, for achieving a beautiful reproduced image and a sufficiently high degree of compression in the vector encoding, the encoding requires significant work and aesthetic (not simply mathematical) precision. For achieving the above-mentioned requirement, editing of vector data is usually conducted with an editing apparatus for graphic patterns.
The conventional systems, however, are simply capable of displaying the data under editing but are incapable of displaying the original data. Consequently the operator is unable to identify the fidelity of the data under editing, in comparison with the original data, so that the editing operation has required considerable skill and has been inefficient in time.
Stated differently, the above-mentioned requirement is incompatible with the work required therefor. Consequently, if the emphasis is given to said requirement, it is customary to draw the original pattern in a large size on a sheet of paper or film and to determine the coordinates of representative points with a tablet or a digitizer. On the other hand, if emphasis is given to the saving of work at encoding, there is proposed a method of A/D converting the original analog pattern for example with a scanning line sensor, then extract the contour and select the characteristic points on the contour with a certain analysis algorithm (Japanese Laid-open Patent No. 58-81383).
However the image input operation with a tablet or a digitizer requires tremendous work, and the precision of the operation is unstable, depending greatly on the quality of the original image and the skill of the operator.
On the other hand, the latter method utilizing A/D conversion and automatic analysis is also associated with the following serious drawbacks:
1. It is not possible to obtain a beautiful reproduced image or a sufficient level of compression if the automatic analyzing algorithm is not complete;
2. An error of at least 2 dots (1 dot at each side of the contour of a certain width) is unavoidable in the thickness of the contour, due to the binary threshold value of the sensor used in the A/D conversion;
3. It is necessary to refine the original analog pattern in order to obtain satisfactory results in the items 1 and 2. This means, in practice, the use of a sufficiently large pattern with sufficiently shaped edges and contours, and the preparation of such pattern may involve significant work which is equivalent to or larger than that required for the input with the digitizer;
4. The original form may be partly or significantly lost if the error is removed as noise for reducing the work in the item 3. For example, in a character " " (which is pronounced as "ke" and means "hair"), the delicately inclined line appearing in the horizontal stroke may be mistaken as a simple horizontal line, or a curved line with a very small curvature may be mistaken as a linear edge.
Therefore, as a practical compromise, the result of the automatic analysis, which in fact performs about 70% of the work actually needed, is further finished with a separate vector pattern editing tool.
In this manner the delicate part, that cannot be automatically analyzied, of the pattern to be encoded, has to be subjected to repeated editing.